Magneto-caloric thermal diode assembly with a rotating heat exchanger

ABSTRACT

A magneto-caloric thermal diode assembly includes a magneto-caloric cylinder. A plurality of thermal stages is stacked along an axial direction between a cold side and a hot side. A heat exchanger includes a cylindrical stator positioned at and in thermal communication with the cold side or the hot side of the plurality of thermal stages. A cylindrical rotor is spaced from the cylindrical stator by a cylindrical gap. The cylindrical rotor is configured to rotate relative to the cylindrical stator about a rotation axis. A shearing liquid zone is defined between a surface of the cylindrical stator that faces the cylindrical gap and a surface of the cylindrical rotor that faces the cylindrical gap when the cylindrical gap is filled with a liquid.

FIELD OF THE INVENTION

The present subject matter relates generally to heat pumps, such as magneto-caloric heat pumps, and heat exchangers for heat pumps.

BACKGROUND OF THE INVENTION

Conventional refrigeration technology typically utilizes a heat pump that relies on compression and expansion of a fluid refrigerant to receive and reject heat in a cyclic manner so as to effect a desired temperature change or transfer heat energy from one location to another. This cycle can be used to receive heat from a refrigeration compartment and reject such heat to the environment or a location that is external to the compartment. Other applications include air conditioning of residential or commercial structures. A variety of different fluid refrigerants have been developed that can be used with the heat pump in such systems.

While improvements have been made to such heat pump systems that rely on the compression of fluid refrigerant, at best such can still only operate at about forty-five percent or less of the maximum theoretical Carnot cycle efficiency. Also, some fluid refrigerants have been discontinued due to environmental concerns. The range of ambient temperatures over which certain refrigerant-based systems can operate may be impractical for certain locations. Other challenges with heat pumps that use a fluid refrigerant exist as well.

Magneto-caloric materials (MCMs), i.e. materials that exhibit the magneto-caloric effect, provide a potential alternative to fluid refrigerants for heat pump applications. In general, the magnetic moments of MCMs become more ordered under an increasing, externally applied magnetic field and cause the MCMs to generate heat. Conversely, decreasing the externally applied magnetic field allows the magnetic moments of the MCMs to become more disordered and allow the MCMs to absorb heat. Some MCMs exhibit the opposite behavior, i.e. generating heat when the magnetic field is removed (which are sometimes referred to as para-magneto-caloric material but both types are referred to collectively herein as magneto-caloric material or MCM). The theoretical Carnot cycle efficiency of a refrigeration cycle based on an MCMs can be significantly higher than for a comparable refrigeration cycle based on a fluid refrigerant. As such, a heat pump system that can effectively use an MCM would be useful.

Challenges exist to the practical and cost competitive use of an MCM, however. In addition to the development of suitable MCMs, equipment that can attractively utilize an MCM is still needed. Currently proposed equipment may require relatively large and expensive magnets, may be impractical for use in e.g., appliance refrigeration, and may not otherwise operate with enough efficiency to justify capital cost.

Accordingly, a heat pump system that can address certain challenges, such as those identified above, would be useful. Such a heat pump system that can also be used in a refrigerator appliance would also be useful.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In an example embodiment, a magneto-caloric thermal diode assembly includes a magneto-caloric cylinder. A plurality of thermal stages is stacked along an axial direction between a cold side and a hot side. Each of the plurality of thermal stages includes a plurality of magnets and a non-magnetic ring. The plurality of magnets is distributed along a circumferential direction within the non-magnetic ring in each of the plurality of thermal stages. The plurality of thermal stages and the magneto-caloric cylinder are configured for relative rotation between the plurality of thermal stages and the magneto-caloric cylinder. A heat exchanger includes a cylindrical stator positioned at and in thermal communication with the cold side or the hot side of the plurality of thermal stages. A cylindrical rotor is spaced from the cylindrical stator by a cylindrical gap. The cylindrical rotor is configured to rotate relative to the cylindrical stator about a rotation axis. A shearing liquid zone is defined between a surface of the cylindrical stator that faces the cylindrical gap and a surface of the cylindrical rotor that faces the cylindrical gap when the cylindrical gap is filled with a liquid.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.

FIG. 1 is a refrigerator appliance in accordance with an example embodiment of the present disclosure.

FIG. 2 is a schematic illustration of certain components of a heat pump system positioned in the example refrigerator appliance of FIG. 1.

FIG. 3 is a perspective view of a magneto-caloric thermal diode according to an example embodiment of the present subject matter.

FIG. 4 is a section view of the example magneto-caloric thermal diode of FIG. 3.

FIG. 5 is a perspective view of the example magneto-caloric thermal diode of FIG. 3 with certain thermal stages removed from the example magneto-caloric thermal diode.

FIG. 6 is a section view of the example magneto-caloric thermal diode of FIG. 5.

FIG. 7 is a perspective view of the example magneto-caloric thermal diode of FIG. 5 with an insulation layer removed from the example magneto-caloric thermal diode.

FIG. 8 is a schematic view of the certain components of the example magneto-caloric thermal diode of FIG. 3.

FIG. 9 is a schematic illustration of certain components of a heat pump system according to another example embodiment of the present subject matter positioned in the example refrigerator appliance of FIG. 1.

FIG. 10 is a schematic view of the certain components of the example magneto-caloric thermal diode of FIG. 3 with heat exchangers positioned at a hot side and a cold side of the example magneto-caloric thermal diode.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

Referring now to FIG. 1, an exemplary embodiment of a refrigerator appliance 10 is depicted as an upright refrigerator having a cabinet or casing 12 that defines a number of internal storage compartments or chilled chambers. In particular, refrigerator appliance 10 includes upper fresh-food compartments 14 having doors 16 and lower freezer compartment 18 having upper drawer 20 and lower drawer 22. Drawers 20, 22 are “pull-out” type drawers in that they can be manually moved into and out of freezer compartment 18 on suitable slide mechanisms. Refrigerator 10 is provided by way of example only. Other configurations for a refrigerator appliance may be used as well including appliances with only freezer compartments, only chilled compartments, or other combinations thereof different from that shown in FIG. 1. In addition, the magneto-caloric thermal diode and heat pump system of the present disclosure is not limited to refrigerator appliances and may be used in other applications as well such as e.g., air-conditioning, electronics cooling devices, and others. Thus, it should be understood that while the use of a magneto-caloric thermal diode and heat pump system to provide cooling within a refrigerator is provided by way of example herein, the present disclosure may also be used to provide for heating applications as well.

FIG. 2 is a schematic view of various components of refrigerator appliance 10, including refrigeration compartments 30 (e.g., fresh-food compartments 14 and freezer compartment 18) and a machinery compartment 40. Refrigeration compartment 30 and machinery compartment 40 include a heat pump system 52 having a first or cold side heat exchanger 32 positioned in refrigeration compartment 30 for the removal of heat therefrom. A heat transfer fluid such as e.g., an aqueous solution, flowing within cold side heat exchanger 32 receives heat from refrigeration compartment 30 thereby cooling contents of refrigeration compartment 30.

The heat transfer fluid flows out of cold side heat exchanger 32 by line 44 to magneto-caloric thermal diode 200. As will be further described herein, the heat transfer fluid rejects heat to magneto-caloric material (MCM) in magneto-caloric thermal diode 200. The now colder heat transfer fluid flows by line 46 to cold side heat exchanger 32 to receive heat from refrigeration compartment 30.

Another heat transfer fluid carries heat from the MCM in magneto-caloric thermal diode 200 by line 48 to second or hot side heat exchanger 34. Heat is released to the environment, machinery compartment 40, and/or other location external to refrigeration compartment 30 using second heat exchanger 34. From second heat exchanger 34, the heat transfer fluid returns by line 50 to magneto-caloric thermal diode 200. The above described cycle may be repeated to suitable cool refrigeration compartment 30. A fan 36 may be used to create a flow of air across second heat exchanger 34 and thereby improve the rate of heat transfer to the environment.

A pump or pumps (not shown) cause the heat transfer fluid to recirculate in heat pump system 52. Motor 28 is in mechanical communication with magneto-caloric thermal diode 200 and is operable to provide relative motion between magnets and a magneto-caloric material of magneto-caloric thermal diode 200, as discussed in greater detail below.

Heat pump system 52 is provided by way of example only. Other configurations of heat pump system 52 may be used as well. For example, lines 44, 46, 48, and 50 provide fluid communication between the various components of heat pump system 52 but other heat transfer fluid recirculation loops with different lines and connections may also be employed. Still other configurations of heat pump system 52 may be used as well.

In certain exemplary embodiments, cold side heat exchanger 32 is the only heat exchanger within heat pump system 52 that is configured to cool refrigeration compartments 30. Thus, cold side heat exchanger 32 may be the only heat exchanger within cabinet 12 for cooling fresh-food compartments 14 and freezer compartment 18. Refrigerator appliance 10 also includes features for regulating air flow across cold side heat exchanger 32 and to fresh-food compartments 14 and freezer compartment 18.

As may be seen in FIG. 2, cold side heat exchanger 32 is positioned within a heat exchanger compartment 60 that is defined within cabinet 12, e.g., between fresh-food compartments 14 and freezer compartment 18. Fresh-food compartment 14 is contiguous with heat exchanger compartment 60 through a fresh food duct 62. Thus, air may flow between fresh-food compartment 14 and heat exchanger compartment 60 via fresh food duct 62. Freezer compartment 18 is contiguous with heat exchanger compartment 60 through a freezer duct 64. Thus, air may flow between freezer compartment 18 and heat exchanger compartment 60 via freezer duct 64.

Refrigerator appliance 10 also includes a fresh food fan 66 and a freezer fan 68. Fresh food fan 66 may be positioned at or within fresh food duct 62. Fresh food fan 66 is operable to force air flow between fresh-food compartment 14 and heat exchanger compartment 60 through fresh food duct 62. Fresh food fan 66 may thus be used to create a flow of air across cold side heat exchanger 32 and thereby improve the rate of heat transfer to air within fresh food duct 62. Freezer fan 68 may be positioned at or within freezer duct 64. Freezer fan 68 is operable to force air flow between freezer compartment 18 and heat exchanger compartment 60 through freezer duct 64. Freezer fan 68 may thus be used to create a flow of air across cold side heat exchanger 32 and thereby improve the rate of heat transfer to air within freezer duct 64.

Refrigerator appliance 10 may also include a fresh food damper 70 and a freezer damper 72. Fresh food damper 70 is positioned at or within fresh food duct 62 and is operable to restrict air flow through fresh food duct 62. For example, when fresh food damper 70 is closed, fresh food damper 70 blocks air flow through fresh food duct 62, e.g., and thus between fresh-food compartment 14 and heat exchanger compartment 60. Freezer damper 72 is positioned at or within freezer duct 64 and is operable to restrict air flow through freezer duct 64. For example, when freezer damper 72 is closed, freezer damper 72 blocks air flow through freezer duct 64, e.g., and thus between freezer compartment 18 and heat exchanger compartment 60. It will be understood that the positions of fans 66, 68 and dampers 70, 72 may be switched in alternative exemplary embodiments.

Operation of heat pump system 52 and fresh food fan 66 while fresh food damper 70 is open, allows chilled air from cold side heat exchanger 32 to cool fresh-food compartment 14, e.g., to about forty degrees Fahrenheit (40° F.). Similarly, operation of heat pump system 52 and freezer fan 68 while freezer damper 72 is open, allows chilled air from cold side heat exchanger 32 to cool freezer compartment 18, e.g., to about negative ten degrees Fahrenheit (−10° F.). Thus, cold side heat exchanger 32 may chill either fresh-food compartment 14 or freezer compartment 18 during operation of heat pump system 52. In such a manner, both fresh-food compartments 14 and freezer compartment 18 may be air cooled with cold side heat exchanger 32.

As may be seen in FIG. 2, refrigerator appliance 10 may include a computing device or controller 80. Controller 80 is operatively coupled or in communication with various components of refrigerator appliance 10. The components include, e.g., motor 28, fresh food fan 66, freezer fan 68, fresh food damper 70, freezer damper 72, etc. Controller 80 can selectively operate such components in response to temperature measurement from a temperature sensor 82. Temperature sensor 82 may, e.g., measure the temperature of fresh-food compartments 14 or freezer compartment 18.

Controller 80 may be positioned in a variety of locations throughout refrigerator appliance 10. For example, controller 80 may be disposed in cabinet 12. Input/output (“I/O”) signals may be routed between controller 80 and various operational components of refrigerator appliance 10. The components of refrigerator appliance 10 may be in communication with controller 80 via one or more signal lines or shared communication busses.

Controller 80 can be any device that includes one or more processors and a memory. As an example, in some embodiments, controller 80 may be a single board computer (SBC). For example, controller 80 can be a single System-On-Chip (SOC). However, any form of controller 80 may also be used to perform the present subject matter. The processor(s) can be any suitable processing device, such as a microprocessor, microcontroller, integrated circuit, or other suitable processing devices or combinations thereof. The memory can include any suitable storage media, including, but not limited to, non-transitory computer-readable media, RAM, ROM, hard drives, flash drives, accessible databases, or other memory devices. The memory can store information accessible by processor(s), including instructions that can be executed by processor(s) to perform aspects of the present disclosure.

FIGS. 3 through 8 are various views of magneto-caloric thermal diode 200 according to an example embodiment of the present subject matter. Magneto-caloric thermal diode 200 may be used in any suitable heat pump system. For example, magneto-caloric thermal diode 200 may be used in heat pump system 52 (FIG. 2). As discussed in greater detail below, magneto-caloric thermal diode 200 includes features for transferring thermal energy from a cold side 202 of magneto-caloric thermal diode 200 to a hot side 204 of magneto-caloric thermal diode 200. Magneto-caloric thermal diode 200 defines an axial direction A, a radial direction R and a circumferential direction C.

Magneto-caloric thermal diode 200 includes a plurality of thermal stages 210. Thermal stages 210 are stacked along the axial direction A between cold side 202 and hot side 204 of magneto-caloric thermal diode 200. A cold side thermal stage 212 of thermal stages 210 is positioned at cold side 202 of magneto-caloric thermal diode 200, and a hot side thermal stage 214 of thermal stages 210 is positioned at hot side 204 of magneto-caloric thermal diode 200.

Magneto-caloric thermal diode 200 also includes a magneto-caloric cylinder 220 (FIG. 8). In certain example embodiments, thermal stages 210 define a cylindrical slot 211, and magneto-caloric cylinder 220 is positioned within cylindrical slot 211. Thus, e.g., each thermal stage 210 may include an inner section 206 and an outer section 208 that are spaced from each other along the radial direction R by cylindrical slot 211 such that magneto-caloric cylinder 220 is positioned between inner and outer sections 206, 208 of thermal stages 210 along the radial direction R. Thermal stages 210 and magneto-caloric cylinder 220 are configured for relative rotation between thermal stages 210 and magneto-caloric cylinder 220. Thermal stages 210 and magneto-caloric cylinder 220 may be configured for relative rotation about an axis X that is parallel to the axial direction A. As an example, magneto-caloric cylinder 220 may be coupled to motor 26 such that magneto-caloric cylinder 220 is rotatable relative to thermal stages 210 about the axis X within cylindrical slot 211 with motor 26. In alternative exemplary embodiments, thermal stages 210 may be coupled to motor 26 such that thermal stages 210 are rotatable relative to magneto-caloric cylinder 220 about the axis X with motor 26.

During relative rotation between thermal stages 210 and magneto-caloric cylinder 220, magneto-caloric thermal diode 200 transfers heat from cold side 202 to hot side 204 of magneto-caloric thermal diode 200. In particular, during relative rotation between thermal stages 210 and magneto-caloric cylinder 220, cold side thermal stage 212 may absorb heat from fresh-food compartments 14 and/or freezer compartment 18, and hot side thermal stage 214 may reject heat to the ambient atmosphere about refrigerator appliance 10.

Each of the thermal stages 210 includes a plurality of magnets 230 and a non-magnetic ring 240. Magnets 230 are distributed along the circumferential direction C within non-magnetic ring 240 in each thermal stage 210. In particular, magnets 230 may be spaced from non-magnetic ring 240 along the radial direction R and the circumferential direction C within each thermal stage 210. For example, each of the thermal stages 210 may include insulation 232, and insulation 232 may be positioned between magnets 230 and non-magnetic ring 240 along the radial direction R and the circumferential direction C within each thermal stage 210. Insulation 232 may limit conductive heat transfer between magnets 230 and non-magnetic ring 240 within each thermal stage 210. As another example, magnets 230 may be spaced from non-magnetic ring 240 along the radial direction R and the circumferential direction C by a gap within each thermal stage 210. The gap between magnets 230 and non-magnetic ring 240 within each thermal stage 210 may limit or prevent conductive heat transfer between magnets 230 and non-magnetic ring 240 within each thermal stage 210.

It will be understood that the arrangement magnets 230 and non-magnetic ring 240 may be flipped in alternative example embodiments. Thus, e.g., a steel and magnet ring may be thermally separate from non-magnetic blocks, e.g., aluminum blocks, within each thermal stage 210. Operation magneto-caloric thermal diode 200 is the same in such configuration.

As may be seen from the above, thermal stages 210 may include features for limiting heat transfer along the radial direction R and the circumferential direction C within each thermal stage 210. Conversely, thermal stages 210 may be arranged to provide a flow path for thermal energy along the axial direction A from cold side 202 to hot side 204 of magneto-caloric thermal diode 200. Such arrangement of thermal stages 210 is discussed in greater detail below.

As noted above, thermal stages 210 includes cold side thermal stage 212 at cold side 202 of magneto-caloric thermal diode 200 and hot side thermal stage 214 at hot side 204 of magneto-caloric thermal diode 200. Thus, cold side thermal stage 212 and hot side thermal stage 214 may correspond to the terminal ends of the stack of thermal stages 210. In particular, cold side thermal stage 212 and hot side thermal stage 214 may be positioned opposite each other along the axial direction A on the stack of thermal stages 210. The other thermal stages 210 are positioned between cold side thermal stage 212 and hot side thermal stage 214 along the axial direction A. Thus, e.g., interior thermal stages 216 (i.e., the thermal stages 210 other than cold side thermal stage 212 and hot side thermal stage 214) are positioned between cold side thermal stage 212 and hot side thermal stage 214 along the axial direction A.

Each of the interior thermal stages 216 is positioned between a respective pair of thermal stages 210 along the axial direction A. One of the respective pair of thermal stages 210 is positioned closer to cold side 202 along the axial direction A, and the other of the respective pair of thermal stages 210 is positioned closer to hot side 204 along the axial direction A. For example, a first one 217 of interior thermal stages 216 is positioned between hot side thermal stage 214 and a second one 218 of interior thermal stages 216 along the axial direction A. Similarly, second one 218 of interior thermal stages 216 is positioned between first one 217 of interior thermal stages 216 and a third one 219 of interior thermal stages 216 along the axial direction A.

Each of the interior thermal stages 216 is arranged to provide a flow path for thermal energy along the axial direction A from cold side thermal stage 212 to hot side thermal stage 214. In particular, magnets 230 of each of interior thermal stages 216 may be spaced from non-magnetic ring 240 of the one of the respective pair of thermal stages 210 along the axial direction A. Thus, e.g., magnets 230 of first one 217 of interior thermal stages 216 may be spaced from non-magnetic ring 240 of second one 218 of interior thermal stages 216 along the axial direction A. Similarly, magnets 230 of second one 218 of interior thermal stages 216 may be spaced from non-magnetic ring 240 of third one 219 of interior thermal stages 216 along the axial direction A. Hot side thermal stage 214 may also be arranged in such a manner.

By spacing magnets 230 of each of interior thermal stages 216 from non-magnetic ring 240 of the one of the respective pair of thermal stages 210 along the axial direction A, conductive heat transfer along the axial direction A from magnets 230 of each of interior thermal stages 216 to non-magnetic ring 240 of an adjacent one of thermal stages 210 towards cold side 202 along the axial direction A may be limited or prevented. In certain example embodiments, magneto-caloric thermal diode 200 may include insulation 250. Magnets 230 of each of interior thermal stages 216 may be spaced from non-magnetic ring 240 of the one of the respective pair of thermal stages 210 along the axial direction A by insulation 250. Insulation 250 may limit conductive heat transfer along the axial direction A from magnets 230 of each of interior thermal stages 216 to non-magnetic ring 240 of an adjacent one of thermal stages 210 towards cold side 202 along the axial direction A.

Magnets 230 of each of interior thermal stages 216 may also be in conductive thermal contact with non-magnetic ring 240 of the other of the respective pair of thermal stages 210. Thus, e.g., magnets 230 of first one 217 of interior thermal stages 216 may be in conductive thermal contact with non-magnetic ring 240 of hot side thermal stage 214. Similarly, magnets 230 of second one 218 of interior thermal stages 216 may be in conductive thermal contact with non-magnetic ring 240 of first one 217 of interior thermal stages 216. Cold side thermal stage 212 may also be arranged in such a manner.

By placing magnets 230 of each of interior thermal stages 216 in conductive thermal contact with non-magnetic ring 240 of the other of the respective pair of thermal stages 210, thermal energy flow along the axial direction A towards hot side 204 may be facilitated, e.g., relative to towards cold side 202. In certain example embodiments, magnets 230 of each of interior thermal stages 216 may be positioned to directly contact non-magnetic ring 240 of the other of the respective pair of thermal stages 210. For example, non-magnetic ring 240 of the other of the respective pair of thermal stages 210 may include projections 242 that extend along the axial direction A to magnets 230 of each of interior thermal stages 216.

The above described arrangement of thermal stages 210 may provide a flow path for thermal energy along the axial direction A from cold side 202 to hot side 204 of magneto-caloric thermal diode 200 during relative rotation between thermal stages 210 and magneto-caloric cylinder 220. Operation of magneto-caloric thermal diode 200 to transfer thermal energy along the axial direction A from cold side 202 to hot side 204 of magneto-caloric thermal diode 200 will now be described in greater detail below.

Magnets 230 of thermal stages 210 produce a magnetic field. Conversely, non-magnetic rings 240 do not produce a magnetic field or produce a negligible magnetic field relative to magnets 230. Thus, each of the magnets 230 may correspond to a high magnetic field zone, and the portion of non-magnetic rings 240 between magnets 230 along the circumferential direction C within each thermal stage 210 may correspond to a low magnetic field zone. During relative rotation between thermal stages 210 and magneto-caloric cylinder 220, magneto-caloric cylinder 220 may be sequentially exposed to the high magnetic field zone at magnets 230 and the low magnetic field zone at non-magnetic rings 240.

Magneto-caloric cylinder 220 includes a magneto-caloric material that exhibits the magneto-caloric effect, e.g., when exposed to the magnetic field from magnets 230 of thermal stages 210. The caloric material may be constructed from a single magneto-caloric material or may include multiple different magneto-caloric materials. By way of example, refrigerator appliance 10 may be used in an application where the ambient temperature changes over a substantial range. However, a specific magneto-caloric material may exhibit the magneto-caloric effect over only a much narrower temperature range. As such, it may be desirable to use a variety of magneto-caloric materials within magneto-caloric cylinder 220 to accommodate the wide range of ambient temperatures over which refrigerator appliance 10 and/or magneto-caloric thermal diode 200 may be used.

Accordingly, magneto-caloric cylinder 220 can be provided with zones of different magneto-caloric materials. Each such zone may include a magneto-caloric material that exhibits the magneto-caloric effect at a different temperature or a different temperature range than an adjacent zone along the axial direction A of magneto-caloric cylinder 220. By configuring the appropriate number sequence of zones of magneto-caloric material, magneto-caloric thermal diode 200 can be operated over a substantial range of ambient temperatures.

As noted above, magneto-caloric cylinder 220 includes magneto-caloric material that exhibits the magneto-caloric effect. During relative rotation between thermal stages 210 and magneto-caloric cylinder 220, the magneto-caloric material in magneto-caloric cylinder 220 is sequentially exposed to the high magnetic field zone at magnets 230 and the low magnetic field zone at non-magnetic rings 240. When the magneto-caloric material in magneto-caloric cylinder 220 is exposed to the high magnetic field zone at magnets 230, the magnetic field causes the magnetic moments of the magneto-caloric material in magneto-caloric cylinder 220 to orient and to increase (or alternatively decrease) in temperature such that the magneto-caloric material in magneto-caloric cylinder 220 rejects heat to magnets 230. Conversely, when the magneto-caloric material in magneto-caloric cylinder 220 is exposed to the low magnetic field zone at non-magnetic rings 240, the decreased magnetic field causes the magnetic moments of the magneto-caloric material in magneto-caloric cylinder 220 to disorient and to decrease (or alternatively increase) in temperature such that the magneto-caloric material in magneto-caloric cylinder 220 absorbs heat from non-magnetic rings 240. By rotating through the high and low magnetic field zones, magneto-caloric cylinder 220 may transfer thermal energy along the axial direction A from cold side 202 to hot side 204 of magneto-caloric thermal diode 200 by utilizing the magneto-caloric effect of the magneto-caloric material in magneto-caloric cylinder 220.

As noted above, the high magnetic field zones at magnets 230 in each of thermal stages 210 (e.g., other than hot side thermal stage 214) is in conductive thermal contact with the low magnetic field zone at the non-magnetic ring 240 of an adjacent thermal stages 210 in the direction of hot side 204 along the axial direction A. Thus, the non-magnetic ring 240 of the adjacent thermal stages 210 in the direction of hot side 204 may absorb heat from the high magnetic field zones at magnets 230 in each of thermal stages 210. Thus, thermal stages 210 are arranged to encourage thermal energy flow through thermal stages 210 from cold side 202 towards hot side 204 along the axial direction A during relative rotation between thermal stages 210 and magneto-caloric cylinder 220.

Conversely, the high magnetic field zones at magnets 230 in each of thermal stages 210 (e.g., other than cold side thermal stage 212) is spaced from the low magnetic field zone at the non-magnetic ring 240 of an adjacent thermal stages 210 in the direction of cold side 202 along the axial direction A. Thus, the non-magnetic ring 240 of the adjacent thermal stages 210 in the direction of cold side 202 is thermally isolated from the high magnetic field zones at magnets 230 in each of thermal stages 210. Thus, thermal stages 210 are arranged to discourage thermal energy flow through thermal stages 210 from hot side 204 towards cold side 202 along the axial direction A during relative rotation between thermal stages 210 and magneto-caloric cylinder 220.

Magneto-caloric thermal diode 200 may include a suitable number of thermal stages 210. For example, thermal stages 210 may include nine thermal stages as shown in FIGS. 3 and 4. In alternative example embodiments, thermal stages 210 may include no less than seven thermal stages. Such number of thermal stages 210 may advantageously permit magneto-caloric cylinder 220 to include a corresponding number of zones with different magneto-caloric materials and thereby allow magneto-caloric thermal diode 200 to operate over a wide range of ambient temperatures as discussed above. Magneto-caloric thermal diode 200 may have an odd number of thermal stages 210.

Each of magnets 230 in thermal stages 210 may be formed as a magnet pair 236. One of magnet pair 236 may be mounted to or positioned at inner section 206 of each thermal stage 210, and the other of magnet pair 236 may be mounted to or positioned at outer section 208 of each thermal stage 210. Thus, magneto-caloric cylinder 220 may be positioned between the magnets of magnet pair 236 along the radial direction Rat cylindrical slot 211. A positive pole of one of magnet pair 236 and a negative pole of other of magnet pair 236 may face magneto-caloric cylinder 220 along the radial direction R at cylindrical slot 211.

Cylindrical slot 211 may be suitably sized relative to magneto-caloric cylinder 220 to facilitate efficient heat transfer between thermal stages 210 and magneto-caloric cylinder 220. For example, cylindrical slot 211 may have a width W along the radial direction R, and magneto-caloric cylinder 220 may having a thickness T along the radial direction R within cylindrical slot 211. The width W of cylindrical slot 211 may no more than five hundredths of an inch (0.05″) greater than the thickness T of magneto-caloric cylinder 220 in certain example embodiments. For example, the width W of cylindrical slot 211 may about one hundredth of an inch (0.01″) greater than the thickness T of magneto-caloric cylinder 220 in certain example embodiments. As used herein, the term “about” means within five thousandths of an inch (0.005″) when used in the context of radial thicknesses and widths. Such sizing of cylindrical slot 211 relative to magneto-caloric cylinder 220 can facilitate efficient heat transfer between thermal stages 210 and magneto-caloric cylinder 220.

Each thermal stage 210 may include a suitable number of magnets 230. For example, each thermal stage 210 may include no less than ten (10) magnets 230 in certain example embodiments. With such a number of magnets 230, may advantageously improve performance of magneto-caloric thermal diode 200, e.g., by driving a larger temperature difference between cold side 202 and hot side 204 relative to a smaller number of magnets 230.

Magnets 230 may also be uniformly spaced apart along the circumferential direction C within the non-magnetic ring 240 in each of thermal stages 210. Further, each of thermal stages 210 may be positioned at a common orientation with every other one of thermal stages 210 within the stack of thermal stages 210. Thus, e.g., first one 217 of interior thermal stages 216 may be positioned at a common orientation with third one 219 of interior thermal stages 216, and hot side thermal stage 214 may be positioned at a common orientation with second one 218 of interior thermal stages 216. As may be seen from the above, the common orientation may sequentially skip one thermal stage 214 with the stack of thermal stages 210. Between adjacent thermal stages 210 within the stack of thermal stages 210, each magnet 230 of thermal stages 210 may be positioned equidistance along the circumferential direction C from a respective pair of magnets 230 in adjacent thermal stages 210.

The non-magnetic rings 240 of thermal stage 210 may be constructed of or with a suitable non-magnetic material. For example, the non-magnetic rings 240 of thermal stage 210 may be constructed of or with aluminum in certain example embodiments. In alternative example embodiments, the non-magnetic rings 240 of thermal stage 210 may be constructed of or with brass, bronze, etc.

Magneto-caloric thermal diode 200 may also include one or more heat exchangers 260. In FIG. 3, heat exchanger 260 is shown positioned at the cold side 202 such that heat exchanger 260 absorbs heat from cold side thermal stage 212. A heat transfer fluid may flow between heat exchanger 260 and cold side heat exchanger 32 via lines 44, 46 as discussed above. Another heat exchanger may be positioned hot side 204 such that a heat transfer fluid may flow between the heat exchanger and hot side heat exchanger 34 via lines 48, 50 as discussed above. The heat exchangers (including heat exchanger 260) may be solid-liquid heat exchangers with a port for heat transfer fluid. Alternatively, the heat exchangers could be direct to solid-gas heat exchangers.

As discussed above, motor 28 is in mechanical communication with magneto-caloric thermal diode 200 and is operable to provide relative rotation between thermal stages 210 and magneto-caloric cylinder 220. In particular, motor 28 may be coupled to one of thermal stages 210 and magneto-caloric cylinder 220, and motor 28 may be operable to rotate the one of thermal stages 210 and magneto-caloric cylinder 220 relative to the other of thermal stages 210 and magneto-caloric cylinder 220.

Motor 28 may be a variable speed motor. Thus, a speed of the relative rotation between thermal stages 210 and magneto-caloric cylinder 220 may be adjusted by changing the speed of motor 28. In particular, a speed of motor 28 may be changed in order to adjust the rotation speed of the one of thermal stages 210 and magneto-caloric cylinder 220 relative to the other of thermal stages 210 and magneto-caloric cylinder 220. Varying the speed of motor 28 may allow magneto-caloric thermal diode 200 to be sized to an average thermal load for magneto-caloric thermal diode 200 rather than a maximum thermal load for magneto-caloric thermal diode 200 thereby providing more efficient overall functionality.

Controller 80 may be configured to vary the speed of motor 28 in response to various conditions. For example, controller 80 may vary the speed of motor 28 in response to temperature measurements from temperature sensor 82. In particular, controller 80 may be vary the speed of motor 28 in a proportional, a proportional-integral, a proportional-derivative or a proportional-integral-derivative manner to maintain a set temperature in fresh-food compartments 14 and/or freezer compartment 18 with magneto-caloric thermal diode 200. As another example, controller 80 may increase the speed of motor 28 from a normal speed based upon a temperature limit, unit start-up, or some other trigger. As yet another example, controller 80 may vary the speed of motor 28 based on any application specific signal from an appliance with magneto-caloric thermal diode 200, such as a humidity level in a dryer appliance, a dishwasher appliance, a dehumidifier, or an air conditioners or when a door opens in refrigerator appliance 10.

FIG. 9 is a schematic illustration of certain components of heat pump system 52 according to another example embodiment of the present subject matter with magneto-caloric thermal diode 200. FIG. 10 is a schematic view of the certain components of magneto-caloric thermal diode 200. In FIGS. 9 and 10, cold side heat exchanger 32 and hot side heat exchanger 34 are coupled to magneto-caloric thermal diode 200. In particular, cold side heat exchanger 32 is coupled to and/or positioned on cold side 202 of magneto-caloric thermal diode 200, and hot side heat exchanger 34 is coupled to and/or positioned on hot side 204 of magneto-caloric thermal diode 200. Cold side heat exchanger 32, e.g., fan 170 of cold side heat exchanger 32 is positioned in refrigeration compartment 30. Conversely, hot side heat exchanger 34, e.g., fan 170 of hot side heat exchanger 34, is positioned in machinery compartment 40. Magneto-caloric thermal diode 200 is positioned within cabinet 12 between refrigeration compartment 30 and machinery compartment 40. Such arrangement may provide a compact heat pump system 52.

While described in greater detail below in the context of refrigerator appliance 10, it will be understood that cold side heat exchanger 32 and/or hot side heat exchanger 34 in combination with magneto-caloric thermal diode 200 may be used in or with any suitable appliance in alternative example embodiments. For example, cold side heat exchanger 32 and/or hot side heat exchanger 34 in combination with magneto-caloric thermal diode 200 may be used in a heat pump water heater, a heat pump dryer, an HVAC unit, etc. In addition, while shown with both cold side heat exchanger 32 and hot side heat exchanger 34 positioned on magneto-caloric thermal diode 200, only one of cold side heat exchanger 32 and hot side heat exchanger 34 may be positioned on magneto-caloric thermal diode 200, and the other of cold side heat exchanger 32 and hot side heat exchanger 34 may be positioned remote from magneto-caloric thermal diode 200. A heat transfer fluid may flow between magneto-caloric thermal diode 200 and the remote heat exchanger in such example embodiments, e.g., in the manner described for FIG. 2. Cold side heat exchanger 32 and/or hot side heat exchanger 34 in combination with magneto-caloric thermal diode 200 may define an axial direction A and a radial direction R that are perpendicular to each other.

Cold side heat exchanger 32 and hot side heat exchanger 34 may both be constructed in the same or similar manner. Thus, for the sake of brevity, only cold side heat exchanger 32 is described in greater detail below. However, it will be understood that hot side heat exchanger 34 may include any or all of the components described below for cold side heat exchanger 32.

With reference to FIG. 10, cold side heat exchanger 32 includes a cylindrical stator 110 and a cylindrical rotor 120. Cylindrical rotor 120 is spaced from cylindrical stator 110 by a cylindrical gap 130. Thus, e.g., cylindrical rotor 120 may not contact cylindrical stator 110 at cylindrical gap 130. Cylindrical rotor 120 is configured to rotate about a rotation axis X relative to cylindrical stator 110. The rotation axis X may be parallel to the axial direction A and perpendicular to the radial direction R. To rotate cylindrical rotor 120, cold side heat exchanger 32 may include a motor 140. Motor 140 is coupled to cylindrical rotor 120 such that motor 140 is operable to rotate cylindrical rotor 120 about the rotation axis X. Motor 140 may also be in mechanical communication with magneto-caloric thermal diode 200 such that motor 140 is operable to provide relative rotation between thermal stages 210 and magneto-caloric cylinder 220. Thus, e.g., motor 140 may correspond to motor 28.

Motor 140 may be a variable speed motor. Thus, e.g., a rotation speed of cylindrical rotor 120 about the rotation axis X may be adjusted by changing the speed of motor 140. Controller 80 may be in operative communication with motor 140, and controller 80 may be operable to adjust the speed of motor 140. The speed of motor 140 may be controlled or set anywhere between and including, for example, zero percent (0%) and one hundred percent (100%). As a particular example, motor 140 may be operable to adjust the rotation speed of cylindrical rotor 120 about the rotation axis X to any suitable speed no less than two hundred and fifty rotations per minute (250 RPM) and no greater than two thousand, five hundred rotations per minute (2500 RPM).

In FIG. 10, cylindrical stator 110 is positioned within cylindrical rotor 120. In particular, cylindrical stator 110 is positioned inside cylindrical rotor 120 and is positioned coaxial with cylindrical rotor 120. It will be understood that the relative position of cylindrical stator 110 and cylindrical rotor 120 may be reversed in alternative example embodiments. Thus, e.g., cylindrical rotor 120 may be positioned within cylindrical stator 110 in alternative example embodiments.

A surface 112 of cylindrical stator 110 is spaced from a surface 122 of cylindrical rotor 120, e.g., along a radial direction R, across cylindrical gap 130. Thus, surface 112 of cylindrical stator 110 and surface 122 of cylindrical rotor 120 face cylindrical gap 130. In FIG. 10, surface 112 of cylindrical stator 110 is an outer surface of cylindrical stator 110, and surface 122 of cylindrical rotor 120 is an inner surface of cylindrical rotor 120.

Cylindrical gap 130 may be filled with a liquid, such as water, propylene glycol, etc., and the liquid may facilitate heat transfer along the radial direction R within cylindrical gap 130 between cylindrical stator 110 and cylindrical rotor 120. For example, the liquid in cylindrical gap 130 may facilitate conductive heat transfer between cylindrical stator 110 and cylindrical rotor 120, e.g., relative to cylindrical gap 130 being filled with a gas, such as air. Thus, the liquid in cylindrical gap 130 may contact both cylindrical stator 110 and cylindrical rotor 120 within cylindrical gap 130, and the liquid may correspond to a heat transfer fluid between cylindrical stator 110 and cylindrical rotor 120 within cylindrical gap 130.

In addition, a shearing liquid zone 160 is defined between cylindrical stator 110 and cylindrical rotor 120. Thus, shearing liquid zone 160 may correspond to the portion of cylindrical gap 130 positioned between surface 112 of cylindrical stator 110 and surface 122 of cylindrical rotor 120, e.g., along the radial direction R. Liquid within shearing liquid zone 160 may shear during rotation of cylindrical rotor 120 relative to cylindrical stator 110, and shearing of the liquid may facilitate convective heat transfer between cylindrical stator 110 and cylindrical rotor 120 via the liquid.

By positioning cold side heat exchanger 32 on magneto-caloric thermal diode 200, e.g., such that cylindrical stator 110 is in conductive thermal communication with cold side 202 of magneto-caloric thermal diode 200, cold side heat exchanger 32 may be produced in a more cost effective manner relative to known heat exchangers that require complex flow circuits. In addition, a size of cold side heat exchanger 32 may be reduced relative to known heat exchangers. For example, cold side heat exchanger 32 may be about half the size of known heat exchangers with similar heat transfer characteristics and that require, e.g., a fan, shroud, spine fins, etc.

Convection heat transfer within cylindrical gap 130 increases with shear rate. Thus, changing the rotational speed of cylindrical rotor 120 about the rotation axis X (e.g., by varying the speed of motor 140 in the manner described above) may likewise change the convection heat transfer along the radial direction R within cylindrical gap 130 between cylindrical stator 110 and cylindrical rotor 120. In particular, increasing the rotational speed of cylindrical rotor 120 about the rotation axis X may increase convection heat transfer along the radial direction R within cylindrical gap 130 between cylindrical stator 110 and cylindrical rotor 120. Conversely, decreasing the rotational speed of cylindrical rotor 120 about the rotation axis X may decrease convection heat transfer along the radial direction R within cylindrical gap 130 between cylindrical stator 110 and cylindrical rotor 120.

A thickness T of shearing liquid zone 160 may be defined along the radial direction R. In certain example embodiments, the thickness T of shearing liquid zone 160 may be no less than about one hundredth of an inch (0.01 inch) and no greater than about one tenth of an inch (0.1 inch). As used herein, the term “about” means within ten percent of the stated thickness when used in the context of thicknesses.

Cold side heat exchanger 32 may include a fan 170. Fan 170 may include a plurality of spaced planar fins 172. Spaced planar fins 172 extend from cylindrical rotor 120, e.g., outwardly along the radial direction R. Cylindrical rotor 120 may for formed of or with a suitable thermally conductive material. For example, cylindrical rotor 120 may be formed from one or more conductive materials, such as aluminum, copper, or tin, as well as alloys thereof. Each planar fin 172 is in conductive thermal communication with cylindrical rotor 120. For example, planar fins 172 may directly contact cylindrical rotor 120. In certain example embodiments, spaced planar fins 172 are separably attached to (e.g., in direct or indirect contact with) cylindrical rotor 120 (e.g., as discrete removable discs). Spaced planar fins 172 may also be formed from a conductive material that is the same or different from the material of cylindrical rotor 120. For instance, spaced planar fins 172 may be formed from stainless steel, aluminum, copper, or tin, as well as alloys thereof.

Spaced planar fins 172 define one or more axial intake channels 174. Axial intake channels 174 may extends through one or more planar fins of spaced planar fins 172, e.g., parallel to the rotation axis X and/or along the axial direction A. Each of the axial intake channels 174 may be positioned at a common radial distance from the rotation axis X.

Spaced planar fins 172 are mounted to cylindrical rotor 120, e.g., such that spaced planar fins 172 rotate with cylindrical rotor 120 about the rotation axis X. As spaced planar fins 172 rotate, fan 170 operates in a manner similar to a so called “Tesla fan.” An airflow (shown with arrows AF on hot side heat exchanger 34 due to space constraints) may be drawn along the axial direction A into axial intake channels 174 when spaced planar fins 172 rotate about the rotation axis X. The airflow AF may flows into axial intake channels 174 from opposite axial ends spaced planar fins 172. Within spaced planar fins 172, the airflow AF passes from axial intake channels 174 to one or more exhaust channels defined between adjacent spaced planar fins 172. The exhaust channels may correspond to axial gaps between adjacent spaced planar fins 172.

From the exhaust channels, the airflow AF is directed outwardly along the radial direction R between spaced planar fins 172 before being exhausted from cold side heat exchanger 32. Advantageously, cold side heat exchanger 32 may promote a heat exchange between spaced planar fins 172 and airflow AF without generating the noise associated with, for example, an axial blower fan. Thus, e.g., the airflow AF may reject heat to spaced planar fins 172 during operation of cold side heat exchanger 32.

As spaced planar fins 172 rotate, viscous forces add energy to the airflow AF between spaced planar fins 172. The boundary layer on spaced planar fins 172 may drive the airflow AF outwardly along the radial direction R. The spacing G along the axial direction A between adjacent spaced planar fins 172 may be selected to facilitate driving of the airflow AF outwardly along the radial direction R between spaced planar fins 172. For example, each spaced planar fin 172 may be spaced from an adjacent spaced planar fin 172 along the axial direction A by no more than about twenty-five micrometers (25 μm). Such spacing may permit operation of fan 170 in the manner described above in certain example embodiments.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A magneto-caloric thermal diode assembly, comprising: a magneto-caloric cylinder; a plurality of thermal stages stacked along an axial direction between a cold side and a hot side, each of the plurality of thermal stages comprises a plurality of magnets and a non-magnetic ring, the plurality of magnets distributed along a circumferential direction within the non-magnetic ring in each of the plurality of thermal stages, the plurality of thermal stages and the magneto-caloric cylinder configured for relative rotation between the plurality of thermal stages and the magneto-caloric cylinder; and a heat exchanger comprising a cylindrical stator positioned at and in thermal communication with the cold side or the hot side of the plurality of thermal stages; a cylindrical rotor spaced from the cylindrical stator by a cylindrical gap, the cylindrical rotor configured to rotate relative to the cylindrical stator about a rotation axis; wherein a shearing liquid zone is defined between a surface of the cylindrical stator that faces the cylindrical gap and a surface of the cylindrical rotor that faces the cylindrical gap when the cylindrical gap is filled with a liquid.
 2. The magneto-caloric thermal diode assembly of claim 1, wherein the cylindrical stator is positioned within the cylindrical rotor.
 3. The magneto-caloric thermal diode assembly of claim 2, wherein the cylindrical stator is positioned coaxial with the cylindrical rotor.
 4. The magneto-caloric thermal diode assembly of claim 1, wherein the heat exchanger further comprises a plurality of spaced planar fins extending from the cylindrical rotor along a radial direction, the plurality of spaced planar fins defining an axial intake channel extending parallel to the rotation axis through one or more planar fins of the plurality of spaced planar fins.
 5. The magneto-caloric thermal diode assembly of claim 4, wherein the axial intake channel is one of a plurality of axial intake channels, and each of the plurality of axial intake channels extends parallel to the rotation axis through one or more planar fins of the plurality of spaced planar fins.
 6. The magneto-caloric thermal diode assembly of claim 5, wherein each of the plurality of axial intake channels is positioned at a common radial distance from the rotation axis.
 7. The magneto-caloric thermal diode assembly of claim 4, wherein each of the plurality of spaced planar fins is spaced from an adjacent one of the plurality of spaced planar fins by an axial gap, the axial gap being no greater than about twenty-five micrometers.
 8. The magneto-caloric thermal diode assembly of claim 1, wherein the shearing liquid zone has a thickness along a radial direction, the thickness of the shearing liquid zone being no less than about one hundredth of an inch and no greater than about one tenth of an inch.
 9. The magneto-caloric thermal diode assembly of claim 1, wherein: a cold side thermal stage of the plurality of thermal stages is positioned at the cold side; a hot side thermal stage of the plurality of thermal stages is positioned at the hot side; each of the plurality of thermal stages between the cold side thermal stage and the hot side thermal stage is positioned between a respective pair of the plurality of thermal stages along the axial direction; one of the respective pair of the plurality of thermal stages is positioned closer to the cold side along the axial direction; the other of the respective pair of the plurality of thermal stages is positioned closer to the hot side along the axial direction; the plurality of magnets of each of the plurality of thermal stages between the cold side thermal stage and the hot side thermal stage is spaced from the non-magnetic ring of the one of the respective pair of the plurality of thermal stages along the axial direction; and the plurality of magnets of each of the plurality of thermal stages between the cold side thermal stage and the hot side thermal stage is in conductive thermal contact with the non-magnetic ring of the other of the respective pair of the plurality of thermal stages.
 10. The magneto-caloric thermal diode assembly of claim 9, wherein the plurality of magnets of each of the plurality of thermal stages between the cold side thermal stage and the hot side thermal stage is spaced from the non-magnetic ring of the one of the respective pair of the plurality of thermal stages along the axial direction by insulation.
 11. The magneto-caloric thermal diode assembly of claim 1, wherein the plurality of magnets is spaced from the non-magnetic ring along the radial direction and the circumferential direction within each of the plurality of thermal stages.
 12. The magneto-caloric thermal diode assembly of claim 11, wherein each of the plurality of thermal stages further comprises insulation positioned between the plurality of magnets and the non-magnetic ring along the radial direction and the circumferential direction.
 13. The magneto-caloric thermal diode assembly of claim 1, wherein the plurality of magnets and the non-magnetic ring of each of the plurality of thermal stages collectively define a cylindrical slot, the magneto-caloric cylinder positioned within the cylindrical slot.
 14. The magneto-caloric thermal diode assembly of claim 13, wherein the cylindrical slot has a width along the radial direction, the magneto-caloric cylinder having a thickness along the radial direction within the cylindrical slot, the width of the cylindrical slot being about one hundredth of an inch greater than the thickness of the magneto-caloric cylinder.
 15. The magneto-caloric thermal diode assembly of claim 1, wherein each of the plurality of magneto-caloric stages has a respective length along the axial direction, the length of one of the plurality of magneto-caloric stages being different than the length of another of the plurality of magneto-caloric stages, each of the plurality of thermal stages having a respective length along the axial direction, the length of each of the plurality of thermal stages corresponding to a respective one of the plurality of magneto-caloric stages.
 16. The magneto-caloric thermal diode assembly of claim 15, wherein the length of each of the plurality of magneto-caloric stages corresponds to a Curie temperature spacing between adjacent magneto-caloric stages of the plurality of magneto-caloric stages.
 17. The magneto-caloric thermal diode assembly of claim 1, wherein the magneto-caloric cylinder further comprises a plurality of insulation blocks, the plurality of magneto-caloric stages and the plurality of insulation blocks distributed sequentially along the axial direction in the order of magneto-caloric stage then insulation block within the magneto-caloric cylinder. 